Study On The Emission Control Of Quantum Dots In LEDs

Semiconductor quantum dots(QDs)have attracted intensive research interests because of their unique photoelectric properties,such as broad absorption range,size depended emission wavelength tunability and high quantum efficiency,which make them promising alternative to the traditional phosphors in lighting and display applications.In particular,cadmium selenide(CdSe)QDs become mainstream material due to their ultra-narrow emitting covering visible region and close-to-unity quantum efficiency.Nevertheless,the synthesis of CdSe QDs still has critical problem in size control that has inflated the total cost and impeded their practical applications.At present,the synthesis of CdSe QDs is controlled by many interacted factors,leading to poor repeatability of size in reaction,and further resulting in poor control of emitting wavelength.In this paper,the method of precise control of QDs size is explored with focusing on the study of reaction mechanism and kinetics of the target ligands in octadecene(ODE)solution through a"green synthesis"approach.We found that a small amount of weak coordinating ligand trioctylphosphine(TOP)can drive fast growth of CdSe QDs into a so-called“size steady”state in which the size change solely depends on temperature rather than other parameters.Based on this discovery,we further our physochemical study on the reaction mechanism and the effect of parameters.All our attmpts lead to the mechanism of in-situ convertion of TOP ligand to a strong coordinating ligand trioctyl-phosphine oxide(TOPO),which bonds tightly to QDs surface and drive the formation of the“steady size”state.Therefore,through the combination of experimental and theoretical verification,a scheme to precisely control of QDs size by controlling the amount of liagand is obtained.Further investigation of the formation of the"steady size"state indicates that the emission wavelength of QDs has approximately linear relationship with the reaction temperature in the form:1/R~2_C=m+K~*_DTWhich provides us the opportunity for the first time to realize the precise wavelength control at sub-nanometer scale with high repeatability.Secondly,based on the prepared QDs,we study the aggregation issue of QDs in the LED package with targeting on the compatibility of QDs with the packaging material organosilicon.Based on the companion's research,we continue to use the method of zinc-terminated polydimethylsiloxane(Zn-PDMS)QDs surface passivation to improve the compatibility of quantum rods(QRs)in silica-gel and synthetic QRs/silicone composites.Our study leads to the further control of the emitting wavelength of QRs in LEDs package.Finally,we intestigate and apply mixed QDs and QRs to fit sun spectral in red region(wavelength range within 590-650 nm)and achieve high quality warm white LEDs with high overall efficiency and minimum efficiency loss in red light region.The above comprehensive research promots the application of QDs in LED lighting and display.